(1) Technical Field
The present invention relates generally to improvements for dial gage instruments used for small displacement measurements, and more particularly, to provide a visual analog readout with means to digitally display and or record the measured values.
(2) Description of the Prior Art
A bore gage is a relevant expression for a measuring tool that is used for measuring the inside diameters of holes. Several types of bore gages are shown in FIGS. 1a, 1b, and FIG. 3. In FIG. 1a a telescopic gage set 100, each with a limited measuring range, are illustrated having different physical dimension as shown in telescopic gages 101, 102, 103 are all used to measure different bore sizes. The telescopic gage can be compared to inside calipers requiring the technician to develop the correct feel to obtain repeatable results. The measured diameter is locked-in by twisting the knurled end of the handle 111 and then transferring the locked-in measured diameter to a remote measuring tool.
FIG. 1b illustrates a set 120 of small hole gages that also require that the adjustments be measured by a remote measuring tool. The small hole gages are initially set smaller than the bore to be measured and then adjusted by rotating a knurled knob until light pressure is felt, indicating to the technician the inside diameter has been reached before removing the gage out of the bore for subsequent measuring by external means.
Of the many methods for mechanically measuring small displacements, the mechanical dial gage is the most popular. This device is used in many applications, for example, dial depth, dial bench, dial O.D, dial snap, dial bore etc., and is familiar to most experimenters and machinists. The units consist of mechanical levers and gears, which suitably amplify the motion, see FIG. 2, showing, schematically, the working parts of a simple dial gage 201. It is apparent that the magnification of the unit shown is equal to (r2/r1)×(r4/r3). By suitable gearing, magnification of the order of 1000 can be achieved, i.e., an input movement 202 of 10−4 inch produces a readable output movement 203 of 10−1 inch.
Referring to FIGS. 3, 4a and 4b, showing a dial bore gage 200 is a dial indicator type that measures a range of holes directly. The tool consists of a range of interchangeable gauging heads 223, in which a precision centralizer having spring loaded contacts 224, and 225 making up a tandem centralizer with an adjustable spring backed contact 226, all three contacts ensuring centering of the gauging head for accurate and repeatable centering while contact 230 transfers horizontal motion to vertical motion by a bell crank motion transfer mechanism that is accurate and linear over its entire range. The vertical motion is transferred to a freely moving rod at its proximal end. A tubular shield 222 contains the rod 231 that transfers axial movement from the gauging head to a dial indicator. The dial indicator 221 mounted and in contact with the distal end of rod 231 measures axial movement of the rod. This combination permits the bore size to be accurately read from the instrument while writing the measured variance to record.